paper

X-Ray Spectral Analysis of Elliptical Galaxies from ASCA: the Fe Abundance in a Multi-Phase Medium

arXiv:astro-ph/9707117 · doi:10.1046/j.1365-8711.1998.01478.x

Abstract

We present spectral analysis of ASCA data of 17 elliptical and 3 lenticular galaxies most of which have high L_x/L_B. Single-temperature models (MEKAL and Raymond-Smith) give unacceptable fits (chi^2_red > 1.5) in most cases and, in agreement with previous studies, give very sub-solar abundances, <Z> = 0.19 +/- 0.12 Z_sun (MEKAL). The spectra for approximately half the sample are better fit with a cooling-flow model which in three cases gives a substantially better fit. The abundances derived from the cooling-flow model are also significantly larger, <Z> = 0.6 +/- 0.5 Z_sun. We empirically tested the reliability of the plasma codes in the Fe-L region and found no evidence for serious problems with the determined temperatures and abundances. Two-temperature models give substantially better fits that are formally acceptable (chi^2_red ~ 1.0) in all but a few cases. The highest S/N galaxies (which also have highest L_x/L_B) have fitted temperatures < 2 keV for both components consistent with each being distinct phases of hot gas. The lowest S/N galaxies (which also have lowest L_x/L_B) generally have a hot component with temperature, T_H > ~5 keV, which is consistent with emission from discrete sources. (We discuss the origin of these two components from analysis of L_x-L_B and L_x/L_B.) The abundances of these two-temperature models are approximately solar, <Z> = 0.9 +/- 0.7 Z_sun (MEKAL), consistent with a recent multi-phase model for the evolution of hot gas in ellipticals. Finally, for several galaxies we find evidence for absorption in excess of the Galactic value and discuss its implications.

20 pages (10 figures). To appear in MNRAS. Some changes made en rout to publication including expanded discussions of the models, the data reduction procedures, and a new section on the evidence and implications for excess absorption

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